Wire coatings and processes for their preparation

ABSTRACT

The present invention relates to wire coatings which contain 
     a) 20 to 50% by weight of a tris-2-hydroxyethyl isocyanurate-modified polyester, 
     b) 2 to 35% by weight of a bismaleimide resin, 
     c) 0.1 to 3% by weight of a catalyst, preferably a titanate catalyst, and 
     d) 35 to 77% by weight of organic solvents, with respect to the total weight of the wire coating, which is 100% by weight. The invention also relates to processes for the preparation of the wire coatings according to the invention.

The present invention relates to wire coatings containing polyestersbased on tris-2-hydroxyethyl isocyanurate, organic solvents, catalysts,auxiliaries and additives. The present invention also relates to aprocess for the preparation of these wire coatings.

Wire coatings based on polyester resins are known and are described, forexample, in U.S. Patent Specification 3,342,780, in U.S. PatentSpecification 3,249,578 and in EP-B-144 281. The polyol component usedin the said publications is tris-2-hydroxyethyl isocyanurate. The use oftris-2-hydroxyethyl isocyanurate (THEIC) in this context leads toparticularly high softening temperatures of the wire coating layer or toa particularly high thermal pressure (IEC 851-6). The wires coated withwire coatings based on polyester resins are distinguished by the factthat the coating film possesses good adhesion to copper wires.

The disadvantage of the wire coatings based on polyester resins comparedwith wire coatings based on polyester-imide resins or polyamide-imideresins is that the wires coated with polyester coatings have a lowthermal shock. THEIC-modified polyester wire coatings are therefore usedas "base coat", onto which, for example, a polyamide-imide wire coatingis applied, in two-coat coatings for wires.

The object on which the present invention is based was to provide wirecoatings which overcome the disadvantages associated with polyester wirecoatings and thus improve the spectrum of properties of theTHEIC-polyester wire coatings. Said wire coatings should be stable onstorage, possess good adhesion to Cu wires and have as high as possiblea thermal pressure as well as an adequate thermal shock. Moreover, thewire coatings should have as high as possible a solids content coupledwith a viscosity favorable for processing. The surface quality of thecoated wires should be improved, in particular with regard to thehardness characteristics.

This object is achieved by means of wire coatings containing polyesterbased on tris-2-hydroxyethyl isocyanurate (THEIC), organic solvents,catalysts, auxiliaries and additives, characterized in that the wirecoatings contain

a) 20 to 50% by weight of the THEIC polyester,

b) 2 to 35% by weight of a bismaleimide resin,

c) 0.1 to 3% by weight of a catalyst, preferably a titanate catalyst,and

d) 35 to 77% by weight of organic solvents, with respect to the totalweight of the wire coating, which is 100% by weight.

It is surprising and was not foreseeable that wire coatings which adherevery well to copper wires and which lead to coatings having outstandingtechnological properties can be obtained by modifying THEIC polyesterwire coatings with bismaleimide resins.

The individual components of the wire coatings according to theinvention are now first explained in more detail below.

The polyesters modified with tris-2-hydroxyethyl isocyanurate (THEIC)(component a)) are known and are described, for example, in U.S. PatentSpecification 3,342,780 and EP-B-144 281. The polyesters are prepared ina known manner by esterification of polybasic carboxylic acids withpolyhydric alcohols in the presence of suitable catalysts. The alcoholcomponents used are, inter alia, tris-2-hydroxyethyl isocyanurate.

In place of the free acid, it is also possible to use ester-formingderivatives thereof.

Alcohols suitable for the preparation of the polyesters are, forexample, ethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-1,3- and1,4-butanediol, 1,5-pentanediol, neopentyl glycol, diethylene glycol,triethylene glycol and also triols, such as, for example, glycerol,trimethylolethane, trimethylolpropane and tris2-hydroxyethylisocyanurate. Mixtures of ethylene glycol and tris-2-hydroxyethylisocyanurate are preferably used. The use of tris-2-hydroxyethylisocyanurate leads to high softening temperatures of the coating layer.

Suitable carboxylic acids are, for example, phthalic acid, isophthalicacid, terephthalic acid and also the esterifiable derivatives thereof,such as, for example, the anhydrides, insofar as these exist, and thelower alkyl esters of the said acids, such as, for example, methyl,ethyl, propyl, butyl, amyl, hexyl and octyl phthalates, terephthalatesand isophthalates. Both the half-esters and the dialkyl esters as wellas mixtures of these compounds can be used. The corresponding acidhalides of these compounds can also be used.

The amounts of the individual components are so chosen that thepolyesters have a ratio of hydroxyl groups to carboxyl groups of from1.1:1 to 2.0:1, preferably from 1.15:1 to 1.60:1.

Catalysts which are suitable for the preparation of the polyesters andwhich are used in amounts of from 0.01 to 5% by weight, with respect tothe feed mixture, are conventional esterification catalysts, such as,for example, heavy metal salts, for example lead acetate and zincacetate, and also organic titanates, for example tetra-n-butyl titanate,cerium compounds and also organic acids, such as, for example,p-toluenesulfonic acid.

Preferably, a polyester a) which is prepared from ethylene glycol,tris-2-hydroxyethyl isocyanurate and dimethyl terephthalate and has ahydroxyl number in the range from 80 to 150 mg KOH/g is used in the wirecoatings according to the invention.

The bismaleimide resins used as component b) of the wire coatingsaccording to the invention are understood to be resins or prepolymerscontaining bismaleimides as units. The bismaleimides are generallyobtained from the bismaleimide units and comonomers (curing agents). Thebismaleimide resins or prepolymers are formed by mixing and heating thebismaleimides and comonomers. Bismaleimide units correspond to thegeneral formula ##STR1## in which Y is an optionally substituted alkenylgroup and X denotes a divalent radical containing at least two carbonatoms. Monomer bismaleimides are disclosed, for example, in DE-A-20 40094, DE-A-27 19 903 and DE-A32 47 058.

Preferred bismaleimide units are 4,4'-bismaleimidodiphenylmethane,4,4'-bismaleimidodiphenyl ether, 3,3'-bismaleimidodiphenyl sulfone,1,3-bismaleimidobenzene, 2,4-bismaleimidotoluene, 1,6-bismaleimidohexaneand 2,2,4-trimethyl-1,6-bismaleimidohexane. In addition tobismaleimides, polymaleimides and also mixtures of differentbismaleimides can be used for the preparation of the bismaleimideresins. The bismaleimides can also contain up to 20% of a monoimide.

Suitable comonomers are alkenyl compounds, aromatic and aliphaticpolyamines, polyphenols, aminophenols, vinyl compounds and allylcompounds. Polyamines suitable as comonomers are, for example, disclosedin DE-A-17 70 867; 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodicyclohexylmethane and 3,3'-diaminodiphenylsulfone are preferred. Usable polyphenols which may be mentioned arebisphenol A, bisphenol F or novolaks; others are listed in DE-A-24 59925. Suitable alkenylphenols or alkenylphenol ethers are described inDE-A-26 27 045; o,o'-diallylbisphenol A is preferred. Oligomeric allyl-or propenyl-terminated sulfones or alkylateddicyclopentadienepolyphenols are also suitable. Usable aminophenols are,for example, m- or p-aminophenol. Examples of vinyl compounds and allylcompounds which may be mentioned are: styrene, divinylbenzene, diallylphthalate, acrylates, methacrylates, diallylbenzene, alkenylphenols,alkenylphenol ethers, triallyl isocyanurate or vinylpyrrolidone. Vinylcompounds and allyl compounds, in particular diallylbisphenol A arepreferred.

Suitable additives are, for example,

fillers, such as chalk, kaolin, ground quartz, dolomite, barite, metalpowders, aluminum oxide hydrate, cement, talc, kieselguhr and pigments,

reinforcing fibers, such as glass, carbon, asbestos and cellulose fibersand also synthetic organic fibers, for example composed of polyethylene,polycarboxylic acid esters, polycarbonate or polyamides,

inhibitors, such as hydroquinones, quinones, nitrobenzenes, N-nitrosocompounds, salts of divalent copper and quaternary ammonium salts,

polymerization initiators, such as benzoyl peroxide, methyl ethyl ketoneperoxide, tert-butyl peroctoate, tert-butyl perbenzoate, cyclohexanoneperoxide, acetylacetone peroxide, perketals, percarbonates, dicumylperoxide, C-C-labile compounds and azo compounds,

curing accelerators, for example copper, lead, calcium, magnesium orcerium octoates or naphthenates and in particular manganese and cobaltoctoates or naphthenates; and also aromatic amines, such asdimethylaniline and diethylaniline, imidazoles, tertiary phosphines andorganic acids,

shrink-reducing polymers, such as polystyrene, polymethyl methacrylate,polyvinyl acetate, polyethylene, polybutadiene and graft copolymers,copolymers and also condensation polymers, such as saturated polyestersor polyester-urethanes,

elastifying additives, for example rubber-like block copolymers andmodified polytetrahydrofuran, and

flame-retardant substances and plasticizers.

In order to prepare the bismaleimide resins b), the starting materialsare mixed using conventional techniques and heated to temperatures ofgenerally 70° to 190° C., a prepolymer forming with a rise in viscoisty,depending on the reaction time. Depending on the type of comonomer andamount of comonomer, a viscous solution or a glassy solidified solid isobtained after cooling and this is either ground or dissolved in asolvent, for example dimethylformamide or N-methylpyrrolidone. Thepreparation of the bismaleimide resins can also be carried out in asolvent.

Suitable bismaleimide resins are described, for example, in DE-A-38 27120, DE-A-38 35 197 and DE-A39 24 867.

The solid, fusible bismaleimide resins disclosed in DE-A-39 24 867 areparticularly preferentially used in the wire coatings according to theinvention. The said resins are prepared from

A) a bismaleimide of the formula ##STR2## where X=CH₂, O or SO₂,

R=C₁ -C₄ -alkyl, and

n=0, 1 or 2,

B) an aminophenol of the formula ##STR3## where m=1 or 2, in a molarratio of A):B) of 2.4:1 to 1.4:1, A) and B) prereacting to form aprepolymer, and also, optionally,

C) 0 to 2% by weight, with respect to A)+B), of a secondary or tertiaryamine or phosphine as addition catalyst,

D) 0 to 1% by weight, with respect to A)+B), of a polymerizationinhibitor,

E) 0 to 25% by weight, with respect to A)+B), of a copolymerizable vinylcompound or allyl compound,

F) 0 to 25% by weight, with respect to A)+B), of an epoxide resincontaining at least 2 epoxide groups, and

G) 0 to 2% by weight, with respect to A)+B), of a peroxide initiator, 70to 90 mol-% of A) and 30 to 60 mol-% of B) being present in unreactedform and the remaining residue having reacted to form the prepolymer.

Suitable bismaleimides A) are the bismaleimide units already mentioned,4,4'-methylene-bis-(N-phenylmaleimide) being preferably used.

Examples of suitable aminophenols B) are m-, o-and molar ratio of A):B)is between 2.4:1 and 1.4:1, preferably between 2.0:1 and 1.5:1 and inparticular between 1.8:1 and 1.6:1.

Suitable catalysts C) are secondary or tertiary amines and phosphinesPreferred amines are N,N,N',N'-tetramethyldiaminodiphenylmethane,N,N-dimethylaniline and dimethylbenzylamine or also imidazoles, such as,for example, 1-methylimidazole. Amongst the phosphines,triphenylphosphine is preferred.

The inhibitors D) used to prevent premature free radical polymerizationof the double bond of the bismaleimide are customary, preferablyphenolic, compounds, in particular hydroquinone or2,6-dimethylhydroquinone in amounts of up to 1, preferably 0.1 to 0.5%by weight, with respect to the sum of A)+B).

Vinyl compounds and allyl compounds E) which are admixed in amounts ofup to 25, preferably of from 5 to 20, % by weight, with respect to thesum of A)+B), are copolymerized as comonomers in the resin matrix duringcuring of the prepreg. They act as diluents to lower the resinviscosity, but, in particular, by means of suitable choice of the natureand amount of these additives, including in the form of mixtures ofseveral vinyl compounds or allyl compounds, it is possible to adjust thetackiness of the prepreg in a targeted manner and to lower the softeningpoint of the resin to room temperature. Monomers which contain two orthree vinyl or allyl groups are preferred. Suitable compounds are, forexample, N-vinylpyrrolidone, N-vinylcarbazole, divinylbenzene,acrylates, diallyl ethers, ethoxylated bisphenol A methacrylate,3,3'-diallyl-bisphenol A, 3,3'-dipropenyl-bisphenol A and also reactionproducts of the diepoxide with acrylic acid or methacrylic acid, but inparticular diallyl phthalate or prepolymers produced therefrom, triallylcyanurate and triallyl isocyanurate.

Conventional epoxide resins F) in amounts of up to 25% by weight, withrespect to A)+B), can also act as reactive diluents which areincorporated in the resin matrix.

0 to 2, preferably 0.01 to 2, % by weight, with respect to the sum ofA)+B), of conventional peroxides which decompose into radicals attemperatures above 180° C. can be added as polymerization initiators G)in order to accelerate the curing process.

The mixture is heated to temperatures of between 140° and 190° C.,preferably to 150°, to 180°, the components melting and bismaleimide andaminophenol reacting with one another. The dwell time of the reactantsat these temperatures should be relatively short, preferably 1 to 10 andin particular 2 to 4 min. The reaction is continued until 70 to 90 mol-%of component A and 30 to 60 mol-% of component B are still present inunreacted form in the resulting bismaleimide resin. The degree ofconversion can be controlled in a simple manner by means of the reactiontemperature, reaction time and, where appropriate, by means of thenature and amount of the addition catalyst. The progress of the reactioncan be monitored by rapid cooling and analytical determination of theunconverted starting components A)+B). In this context, high pressureliquid chromatography (HPLC) is used for quantitative determination ofA+B in the resin mixture, the retention times and areas having beencalibrated beforehand using the pure substances A and B. Afterterminating the reaction, the melt is cooled rapidly. The resin can begranulated or converted to flakes or powder.

With regard to further details on the preparation of the bismaleimideresins b) preferably used in the wire coatings according to theinvention, reference is made to corresponding explanations in DE-A-39 24867.

In addition, bismaleimide resins b) which contain

A) a bismaleimide,

B) a heterocyclic comonomer of the formula

    R--Ar--O--Het--O--Ar--R

where

R=an alkenyl or alkenyloxy group having 3-6 C atoms,

Ar=a phenylene, naphthylene or ##STR4## where X=O, S, SO₂, CO, C(R')₂(R'=H, C₁ -C₆ -alkyl, CF₃ or phenyl) or a chemical bond, it beingpossible for Ar optionally to carry a hydroxyl group, and

Het=a heterocyclic six-membered ring selected from the group comprising##STR5## are particularly preferentially used in the wire coatingsaccording to the invention. Bismaleimide resins of this type aredescribed in DE-A-3,827,120.

Suitable comonomers B ) are, for example,2,6-bis-(3-allyl-4-hydroxyphenoxy) pyridine,2,6-bis-(3-allyloxyphenoxy)pyridine,2,6-bis-(4-allyl-3-hydroxyphenoxy)pyridine,2,6-bis-[(3-allyl-4-hydroxyphenylisopropyl)-phenoxy]pyridine and thecorresponding pyridazine derivatives. The heterocyclic comonomerparticularly preferentially used is 2,6-bis-(2-propenylphenoxy)pyridine.Suitable preparation processes are described in DE-A-3,827,120.

With regard to suitable bismaleimide monomers, reference is made to theexamples given above.

For preparation of the bismaleimide resins, the starting materials aremixed using the conventional techniques and heating to temperatures ofbetween 70 and 190° C., a prepolymer being formed. Depending on theextent to which prepolymerization proceeds, a melt of relativelyviscosity or a glassy solidified solid, which is ground or dissolved ina solvent, is obtained. The preparation of the resins can also becarried out in a solvent.

The mixing ratio for the reaction of the bismaleimide with theheterocyclic alkenyl compound can be chosen relatively freely, anequivalent ratio of 1 to 0.05 to 5 being preferable.

Further components can be added to the bismaleimide resins described.Suitable additive components are, for example, amines, preferablyaromatic diamines (for example 4,4'-diaminodiphenylmethane) andaminophenols, which are also able to enter into an addition reactionwith the maleimide double bonds. Prepolymers, for example of a bisimideand an amine, can also be used.

Further components which can be co-used in a proportion of up to 50% byweight, with respect to the mixture, are suitable vinyl monomers, forexample styrene, α-methylstyrene, divinylbenzene, acrylic acid esters ormethacrylic acid esters, diallyl phthalate, 3,3'-diallylbisphenol A,triallyl isocyanurate, triallyl cyanurate or vinylpyrrolidone.

With regard to further details, reference is made to correspondingexplanations in DE-A-38 27 120. The bismaleimide resins disclosed inthis published specification are preferably used since they have lowsoftening points and a long gelling time, which facilitates processingin the melt state.

In addition to the bismaleimide resins described, a large number offurther BMI resins are suitable for use in the wire coatings accordingto the invention.

The bismaleimide resins used in the wire coatings according to theinvention are, for example, obtainable under the trade names Palimid® Sfrom BASF AG, such as, for example, the bismaleimide resins Palimid® S410 KR, Palimid® S 420 KR, Palimid® S 430 KR, Palimid® S 440 KR,Palamid® S 450 KR and Palimid® S 460 KR. Palimid® S 410 KR, Palimid® S430 KR and Palimid® S 440 KR (BASF AG) are particularly preferred.

Organic solvents (component d) which are suitable for the wire coatingsaccording to the invention and which can also already be used for thepreparation of the THEIC polyesters are cresol and non-cresol organicsolvents, such as, for example, cresol, phenol, gylcol ethers, such as,for example, methyl glycol, ethyl glycol, isopropyl glycol, butylglycol, methyl diglycol, ethyl diglycol and butyl diglycol; glycol etheresters, such as, for example, methyl glycol acetate, ethyl glycolacetate, butyl glycol acetate and 3-methoxy-n-butyl acetate; cycliccarbonates; such as, for example, propylene carbonate; cyclic esters,such as, for example, γ-butyrolactone, and also, for example,dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone. Inaddition, aromatic solvents can also be used, optionally in combinationwith the said solvents.

The organic solvents can be partially replaced by extenders. Preferably,either pure solvent or a pure solvent mixture or solvents containing upto 40% by weight, with respect to the total weight of component d), ofextenders are used. Examples of suitable extenders are xylene,Solventnaphtha®, toluene, ethylbenzene, cumene, benzene homologs,various Solvesso® and Shellsol® grades and Deasol®.

The wire coatings according to the invention contain 0.1 to 3% byweight, with respect to the total weight of the wire coating includingthe catalyst, of a transesterification catalyst, preferably a titanatecatalyst (component c)), such as, for example, tetraalkyl titanates, forexample tetraisopropyl titanate, tetrapropyl titanate, tetrabutyltitanate, tetraamyl titanate, tetrahexyl titanate, tetraethyl titanate,tetramethyl titanate or diisopropyl dibutyl titanate, or aryl titanates,such as tetraphenyl titanate, tetracresyl titanate, tetraxylenyltitanate or also triethanolamine titanate. Crosslinking catalysts whichare also suitable are heavy metal salts, such as lead acetate, zincacetate, cerium compounds and also organic acids, such as, for example,p-toluenesulfonic acid.

Advantageously, the wire coatings according to the invention contain 0.2to 5.0% by weight of a flow-promoting phenol-formaldehyde resin e), withrespect to the total weight of the wire coating including component e).

Suitable phenolic resins are known condensation products of phenol,substituted phenols or bisphenol A with formaldehyde. The properties ofthe phenolic resins depend on the nature of the phenol component and ofthe aldehyde component, of the value to which the pH is adjusted duringthe preparation and on the ratio of the two reactants. According to thepresent invention, the phenolic resins can also be modified byincorporation of other compounds during the polycondensation reaction aswell as by subsequent modification of the phenolic resin and differentcontrol of the reaction process. Of course, in addition to thecondensation products with formaldehyde, those with other aldehydes canalso be used.

It is furthermore advantageous that the wire coatings according to theinvention contain up to 0.3% by weight of imidazole or of an imidazolederivative f), with respect to the total weight of the wire coatingsincluding the component f). Suitable imidazole derivatives are, forexample, methylimidazole and 1,2-dimethylimidazole. In addition, it ispreferred that the wire coatings contain up to 0.3% by weight of atertiary amine g), with respect to the total weight of the wire coatingincluding g). Suitable tertiary amines are N-methylmorpholine,N-methylpyrrolidine, N-methylpyrrole, trimethylamine, triethylamine,dimethylethanolamine, diethylmethylamine, methyldiethanolamine,ethylmethylethanolamine, dimethylethylamine, dimethylpropylamine,dimethyl3-hydroxy-1-propylamine, dimethylbenzylamine,dimethyl-2-hydroxy-1-propylamine, dimethyl-1-hydroxy-2-propylamine and1,4-diazabicyclo[2.2.2 ]octane.

In addition, the wire coatings can also contain conventional auxiliariesand additives in the customary amounts, preferably up to 1% by weight,with respect to the total weight of components a) and b). Examples ofauxiliaries which can be used for the wire coatings are flow-promotingmelamine resins or flow agents based on polyacrylates.

Wire coatings according to the invention which contain

a) 28 to 47% by weight of the THEIC polyester,

b) 4 to 10% by weight of a bismaleimide resin,

c) 0.3 to 1.5% by weight of a titanate catalyst,

d) 40 to 67% by weight of organic solvents,

e) 0.4 to 4.0% by weight of a phenol-formaldehyde resin,

f) 0.01 to 0.2% by weight of imidazole and/or of an imidazole derivativeand

g) 0.01 to 0.2% by weight of a tertiary amine, with respect to the totalweight of the wire coating, which is 100% by weight, lead to coatingswhich have particularly good properties.

The present invention also relates to a process for the preparation ofthe wire coatings described above, which is characterized in that thepolyester component a), the bismaleimide resin b), the catalyst c),organic solvent d), optionally the phenolic resin component e),optionally the imidazole or the imidazole derivative f), optionally thetertiary amine g) and also further auxiliaries and additives areprocessed by mixing and, where appropriate, dispersing to give a wirecoating composition.

In this context, a process for the preparation of the wire coatingsaccording to the invention is preferred which is characterized in thatthe THEIC-modified polyester a) is dissolved in an organic solvent, thebismaleimide resin b) is added, either in the form of a solid or inorganic solution, to the polyester resin solution and the components c),optionally d), optionally e), optionally f) and optionally g), as wellas further auxiliaries and additives are added. If appropriate, theviscosity is then also adjusted to the desired value using additionalsolvent.

Modifications of this preparation process are also possible. Thus, forexample the THEIC polyester a) can be dissolved together with thebismaleimide resin.

The wire coatings are applied and cured using conventional wire coatingmachines. The particular coating film thickness required is built up byat least 1 to up to 10 individual applications, each individual coatingapplication being completely cured bubble-free before applying a freshcoating. Conventional coating machines operate at take-off speeds of 5to 180 m/min, depending on the binder base of the coating compositionand depending on the thickness of the wire to be coated. Typical oventemperatures are between 300 and 550° C. Wire coating machines of thistype are known and therefore do not need to be explained in more detailhere.

The wire coatings according to the invention are surprisingly stable onstorage although they contain such diverse components as THEICpolyester, bismaleimide resins, titanates and optionally phenolicresins. The wire coating coverings obtained from the coatings accordingto the invention after coating and stoving have very good adhesion tocopper wires although--as is shown below--bismaleimide resins on theirown, that is to say without the polyester component a), lead tonon-adherent coatings. Surprisingly, it has been found that the wirecoatings resulting from the coatings according to the invention have anexceptionally good spectrum of properties. Thus, the wires coated withthe coatings according to the invention show, in particular, outstandingresults with respect to thermal shock.

The invention is illustrated in more detail below with reference toillustrative embodiments.

A) Preparation of a THEIC polyester resin

A polyester resin having a hydroxyl number of 90 to 140 mgKOH/g isprepared from 125.84 g of ethylene glycol, 294.92 g oftris-2-hydroxyethyl isocyanurate, 578.57 g of dimethyl terephthalate and0.68 g of butyl titanate by heating to 200° C. This THEIC-modifiedpolyester resin is used in the following illustrative embodiments.

B) Preparation of a THEIC polyester coating

355.60 g of the THEIC-modified polyester prepared under A) are dissolvedin 264.80 g of cresol at 150° C. with stirring. After cooling to roomtemperature, 15.00 g of butyl titanate, 54.30 g of Solventnaphtha and42.62 g of a commercially available phenolic resin are added and themixture is diluted with 214.4 g of cresol and 53.54 g of Solventnaphtha.Viscosity (23° C.): 540 mPas Solids content (1 g, 1 h, 180° C.): 39.8%.

C) Preparation of a bismaleimide resin coating

253.33 g of cresol are added to 366.12 g of a bismaleimide resin basedon monomeric bismaleimides and aminophenols and the mixture is stirredat room temperature until all of the bismaleimide resin has dissolved.After adding 0.62 g of 1,2-dimethylimidazole, 126.78 g of solventnaphthaand 253.15 g of cresol, the coating is stirred for 6 hours and thenfiltered. Viscosity (23° C): 546 mPas Solids content (1 g, 1 h, 180°C.): 37.6%.

EXAMPLE 1

37.04 g of a bismaleimide resin based on monomeric bismaleimides andaminophenols and 0.04 g of 1,2-dimethylimidazole are added at roomtemperature, with stirring, to 925.89 g of the THEIC-modified polyesterresin coating prepared under B). After adding 27.77 g of cresol and 9.26g of Solventnaphtha, the coating is stirred for 6 hours and thenfiltered. Viscosity (23° C.): 640 mPas Solids content (1 g, 1 h, 180°C.): 40.6%

EXAMPLE 2

71.42 g of a bismaleimide resin based on monomeric bismaleimides andaminophenols and 0.07 g of 1,2-dimethylimidazole are added at roomtemperature, with stirring, to 892.79 g of the THEIC-modified polyesterresin coating prepared under B). After adding 26.79 g of cresol and 8.93g of Solventnaphtha, the coating is stirred for 6 hours and thenfiltered. Viscosity (23° C.)=815 mPas Solids content (1 g, 1 h, 180°C.): 41.1%

EXAMPLE 3

81.80 g of a bismaleimide resin based on monomeric bismaleimides andaminophenols are dissolved in 75.00 g of cresol and 24.99 g ofSolventnaphtha. The viscosity of this solution is 630mPas at 23° C. Thesolution is added, with stirring, at room temperature to 818.05 g of theTHEIC-modified polyester coating prepared under B). After adding 0.16 gof 1,2-dimethylimidazole, the coating is stirred for 2 hours and thenfiltered. Viscosity (23° C.): 540 mPas Solids content (1 g, 1 h, 180°C.): 39.6%

EXAMPLE 4

97.61 g of a bismaleimide resin based on monomeric bismaleimides andaminophenols are dissolved in 23.76 g of cresol at 75° C., withstirring. The viscosity of the solution is 35 Pas at 23° C. Aftercooling to 50° C., 813.38 g of the polyester coating prepared under B),0.12 g of 1,2-dimethylimidazole, 48.86 g of cresol and 16.29 g ofsolventnaphtha are added and the coating is stirred for 2 hours and thenfiltered. Viscosity (23° C.): 695 mPas Solids content (1 g, 1 h, 180°C.): 41.2%

EXAMPLE 5

139.35 g of a bismaleimide resin based on monomeric bismaleimides andaminophenols are dissolved in 33.93 g of cresol at 75° C., withstirring. After cooling to 50° C., 696.77 g of the THEIC-modifiedpolyester coating prepared under B), 0.14 g of 1,2-dimethylimidazole,97.37 g of cresol and 32.44 g of solventnaphtha are added. The resultingcoating is stirred for 2 hours and then filtered. Viscosity (23° C.):650 mPas Solids content (1 g, 1 h, 180° C.): 40.5%.

The coatings prepared under B) and C) and in Examples 1 to 5 are appliedas coatings in a standard wire coating machine. Coating conditions: KLHoven, Aumann Length: 4 m Temperature: 500° C. Application system:pump+felt Wire diameter: 0.71 mm Take-off speed: 28 m/min Number ofpasses: 8 Degree of increase: 2 L

The coated wires are tested in accordance with IEC 851. The results aresummarized in the following Table:

    __________________________________________________________________________            B      C                                                                      (Comparison                                                                          (Comparison                                                    Example example)                                                                             example)                                                                             1     2     3     4     5                               __________________________________________________________________________    Color shade                                                                           red-brown                                                                            light brown                                                                          red-brown                                                                           dark brown                                                                          ruby  dark brown                                                                          dark brown                      Surface good   good   good  good  very good                                                                           very good                                                                           very good                       Adhesion on                                                                           25%    no adhesion                                                                          25%   25%   25%   25%   10%                             winding,       on the wire                                                    1 × d +                                                                 pre-expansion                                                                 Thermal shock                                                                         155° C.                                                                              155° C.                                                                      200° C.                                                                      185° C.                                                                      220° C.                                                                      220° C.                  1 × d,                                                                  30 min                                                                        Thermal 420° C.                                                                              440° C.                                                                      430° C.                                                                      440° C.                                                                      450° C.                                                                      450° C.                  pressure                                                                      tg s    124° C.                                                                              138° C.                                                                      142° C.                                                                      146° C.                                                                      137° C.                                                                      136° C.                  steep rise                                                                    Hardness                                                                              3-4 H         4 H   4 H   4-5 H 4-5 H 4-5 H                           __________________________________________________________________________

The wire coated with a THEIC polyester coating (Comparison example B) isdistinguished by very good adhesion on winding 1×d with a pre-expansionof 25%. A relatively weak thermal shock 1×d of 155° C. is adisadvantage.

The bismaleimide resin coating described under C) has no adhesion tocopper wires.

The wire coatings according to the invention prepared in Examples 1-5have a good adhesion to the copper wire which corresponds to thestandard. The surface quality of the coated wires and the hardness ofthe coating film are in some cases superior compared with conventionalTHEIC polyester-coated wires.

However, the wire coatings according to the invention are distinguishedin particular by the fact that the wires coated therewith have a thermalpressure of 430°-450° C. and a thermal shock, 1×d of up to 220° C. Thetan S steep rise is between 136° C. and 146° C.

We claim:
 1. A wire coating comprising polyester based ontris-2-hydroxyethyl isocyanurate, organic solvents, catalysts,auxiliaries and additives, characterized in that they coatingcomprisesa) 20 to 50% by weight of a polyester based ontris-2-hydroxyethyl isocyanurate which has a hydroxyl/carboxyl groupsratio of 1.1:1 to 2.0:1, b) 2 to 35% by weight of a bismaleimide resin,which is prepared fromA) a bismaleimide of the formula ##STR6## whereX=CH₂, O or SO₂, R=C₁ -C₄ -alkyl, and n=0, 1 or 2, l and B anaminophenol of the formula ##STR7## where m=1 or 2, in a molar ratio ofA):B) of 2.4:1 to 1.4:1, A) and B) prereacting to form a prepolymer, andalso, optionally, C) 0 to 2% by weight, with respect to A)+B), of asecondary or tertiary amine or phosphine as addition catalyst, D) 0 to1% by weight, with respect to A)+B), of a polymerization inhibitor, E) 0to 25% by weight, with respect to A)+B), of a copolymerizable vinylcompound or allyl compound, F) 0 to 25% by weight, with respect toA)+B), of an epoxide resin containing at least 2 epoxide groups, and G)0 to 2% by weight, with respect to A)+B), of a peroxide initiator, 70to90 mol-% of A) and 30 to 60 mol-% of B) being present in unreacted formand the remaining residue having reacted to form the prepolymer, c) 0.1to 3% by weight of a catalyst, d) 35 to 77% by weight of organicsolvents, e) optionally, 0.2 to 5.0% by weight of a phenolic resin, f)optionally, up to 0.3% by weight of imidazole or an imidazole containingcompound and g) optionally, up to 0.3% by weight of a tertiary amine,with respect to the total weight of the wire coating, which is 100% byweight.
 2. A wire coating according to claim 1, comprisinga) 28 to 47%by weight of component a), b) 4 to 10% by weight of component b), c) 0.3to 1.5% by weight of a titanate catalyst, d) 40 to 67% by weight ofcomponent d), e) 0.4 to 4.0% by weight of a phenol-formaldehyde resin,f) 0.01 to 0.2% by weight of component f) and g) 0.01 to 0.2% by weightof component g).
 3. A wire coating according to claim 1, whereincomponent a) is prepared from ethylene glycol, tris-2-hydroxyethylisocyanurate and dimethyl terephthalate and has a hydroxyl number from80 to 150 mg KOH/g.
 4. A process for the preparation of a wire coatingcomposition comprisinga) 20 to 50% by weight of a polyester based ontris-2-hydroxyethyl isocyanurate which has a hydroxyl/carboxyl groupsratio of 1.1:1 to 2.0:1, b) 2 to 35% by weight of a bismaleimide resin,which is prepared fromA) a bismaleimide of the formula ##STR8## whereX=CH₂, O or SO₂,R=C₁ -C₄ -alkyl, and n=0, 1 or 2, and B) an aminophenolof the formula ##STR9## where m=1 or 2, in a molar ratio of A):B) of2.4:1 to 1.4:1, A) and B) prereacting to form a prepolymer, and also,optionally, C) 0 to 2% by weight, with respect to A)+B), of a secondaryor tertiary amine or phosphine as addition catalyst, D) 0 to 1% byweight, with respect to A)+B), of a polymerization inhibitor, E) 0 to25% by weight, with respect to A)+B), of a copolymerizable vinylcompound or allyl compound, F) 0 to 25% by weight, with respect toA)+B), of an epoxide resin containing at least 2 epoxide groups, and G)0 to 2% by weight, with respect to A)+B), of a peroxide initiator, 70 to90 mol-% of A) and 30 to 60 mol-% of B) being present in unreacted formand the remaining residue having reacted to form the prepolymer, c) 0.1to 3% by weight of a catalyst, d) 35 to 77% by weight of organicsolvents, e) optionally, 0.2 to 5.0% by weight of a phenolic resin, f)optionally, up to 0.3% by weight of imidazole or imidazole containingcompound and g) optionally, up to 0.3% by weight of a tertiary amine,with respect to the total weight of the wire coating, which is 100% byweight, said process comprising the steps of mixing components a)-g),where components a) and b)are mixed at room temperature, and optionallydispersing to give a wire coating composition.
 5. The wire coatingcomposition of claim 1, wherein the imidazole containing compound (f) isselected from the group consisting of methylimidazole and1,2-dimethylimidazole.
 6. The process of claim 4, wherein the imidazolecontaining compound (f) is selected from the group consisting ofmethylimidazole and 1,2-dimethylimidazole.
 7. A process for thepreparation of a wire coating composition comprisinga) 20 to 50% byweight of a polyester based on tris-2-hydroxyethyl isocyanurate whichhas a hydroxyl/carboxyl groups ratio of 1.1:1 to 2.0:1, b) 2 to 35% byweight of a bismaleimide resin, which is prepared fromA) a bismaleimideof the formula ##STR10## where X=CH₂, O or SO₂,R=C₁ -C₄ -alkyl, and n=0,1 or 2, and B) an aminophenol of the formula ##STR11## where m=1 or 2,in a molar ratio of A):B) of 2.4:1 to 1.4:1, A) and B) prereacting toform a prepolymer, and also, optionally, C) 0 to 2% by weight, withrespect to A)+B), of a secondary or tertiary amine or phosphine asaddition catalyst, D) 0 to 1% by weight, with respect to A)+B), of apolymerization inhibitor, E) 0 to 25% by weight, with respect to A)+B),of a copolymerizable vinyl compound or allyl compound, F) 0 to 25% byweight, with respect to A)+B), of an epoxide resin containing at least 2epoxide groups, and G) 0 to 2% by weight, with respect to A)+B), of aperoxide initiator, 70 to 90 mol-% of A) and 30 to 60 mol-% of B) beingpresent in unreacted form and the remaining residue having reacted toform the prepolymer, c) 0.1 to 3% by weight of a catalyst, d) 35 to 77%by weight of organic solvents, e) optionally, 0.2 to 5.0% by weight of aphenolic resin, f) optionally, up to 0.3% by weight of imidazole orimidazole containing compound and g) optionally, up to 0.3% by weight ofa tertiary amine, with respect to the total weight of the wire coating,which is 100% by weight,said process comprising the steps of mixingcomponents a) wherein components a), and b) are mixed at a temperatureof 50° C. and optionally dispersing to give a wire coating composition.